U.S. patent number 4,506,553 [Application Number 06/538,071] was granted by the patent office on 1985-03-26 for apparatus for measuring small values of air flow.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Charles W. Bruce, Kenneth E. Kunkel, Fred C. Webb.
United States Patent |
4,506,553 |
Bruce , et al. |
March 26, 1985 |
Apparatus for measuring small values of air flow
Abstract
A gas flow rotor cyclically connects a microphone to a dynamic
flow press and then a reference static flow pressure. The
microphone converts the pressures to a resultant alternating
differential signal providing a first input to a phase-locked
amplifier. A second amplifier input is derived from an optical
pickup mounted on the rotor. Only the AC component of the converted
microphone signal, which has a fixed phase relationship to that of
the rotor, is amplified. A readout connected in circuit with the
amplifier indicates the dynamic flow pressure.
Inventors: |
Bruce; Charles W. (Las Cruces,
NM), Kunkel; Kenneth E. (Las Cruces, NM), Webb; Fred
C. (Las Cruces, NM) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
24145349 |
Appl.
No.: |
06/538,071 |
Filed: |
September 30, 1983 |
Current U.S.
Class: |
73/861.65;
73/170.14; 73/861.18 |
Current CPC
Class: |
G01F
1/36 (20130101) |
Current International
Class: |
G01F
1/34 (20060101); G01F 1/36 (20060101); G01F
001/36 (); G01P 005/17 () |
Field of
Search: |
;73/861.18,861.65,861.67,861.68,182,189 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2911928 |
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Oct 1980 |
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DE |
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0396573 |
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Jan 1974 |
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SU |
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Primary Examiner: Ruehl; Charles A.
Attorney, Agent or Firm: Lane; Anthony T. Gibson; Robert P.
Elbaum; Saul
Government Interests
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured, used, and
licensed by or for the United States Government for governmental
purposes without the payment to us of any royalty thereon.
Claims
We claim:
1. A sensor for measuring gas flow comprising:
a housing having
(a) a first orifice for receiving dynamic gas flow
therethrough,
(b) a second orifice spaced from the first and communicating with a
static gas or other reference environment,
(c) a third orifice spaced from the other two and communicating
with a microphone;
rotor means located inwardly of the housing and having first and
second curved passageways therein for alternately completing a
passage between the third orifice, and the first then second
orifices thus subjecting the microphone to a resultant acoustic
wave dependent upon the dynamic gas flow.
2. The subject matter of claim 1 together with means mounted in the
housing and adjacent the rotor means for photo-optically detecting
the rotation of the rotor means.
3. The structure set forth in claim 2 together with a phase-locked
amplifier having first and second inputs, said first input being
connected to said microphone, and said second input being connected
to the output of said photo-optic detecting means.
4. The subject matter set forth in claim 3 with indicating means
connected in circuit with the output of the amplifier for
displaying gas flow data.
5. A sensor for measuring air flow comprising:
a housing having a first inlet;
means for directing dynamic ambient air pressure to the inlet;
an outlet in the housing spaced from the first inlet;
a microphone located adjacent the outlet;
rotor means located in the housing for connecting the first inlet
and the outlet at a preselected position of the rotor means thereby
subjecting the microphone to the dynamic ambient air pressure
condition at the first inlet;
a second inlet in the housing spaced from the first inlet;
means connecting the second inlet with an external static or other
airflow reference; and
means rotating the rotor means to another position for causing the
microphone to sense a second pressure condition corresponding to
the airflow reference.
6. The subject matter set forth in claim 5 together with means
mounted in the housing and adjacent the rotor means for
photo-optically detecting the rotation of the rotor means.
7. The subject matter set forth in claim 6 further comprising a
phase-locked amplifier having first and second inputs, said first
input being connected to said microphone, and said second input
being connected to the output of said photo-optic detecting
means.
8. The subject matter set forth in claim 7 wherein the means
rotating the rotor means comprises a motor coaxially mounted to the
housing and having a shaft passing through the housing for
connection to the rotor means.
9. The subject matter set forth in claim 8 together with means for
changing a signal at the output of the amplifier to a digital
signal.
10. The subject matter set forth in claim 9 together with display
means connected to the changing means output for indicating values
of measured dynamic air flow.
Description
FIELD OF THE INVENTION
The present invention relates to manometers and more particularly
to a high sensitivity and fast response manometric air flow
sensor.
BRIEF DESCRIPTION OF THE PRIOR ART
In a number of scientific applications, it is important to obtain
accurate readings of very low and/or rapidly fluctuating air flow
rates while retaining a large dynamic range. Unfortunately,
conventional air flow sensors are neither sensitive to small flow
rates nor do they have fast time response. Further, when used in
meteorological applications, harsh environments exist which have
hampered the design of a satisfactory instrument.
BRIEF DESCRIPTION OF THE PREFERRED INVENTION
The present invention has been designed for sensitivity to small
flow rates with a fast response time while disturbing that low flow
minimally. The present sensor measures the difference between a
dynamic wind pressure at an orifice facing into the wind and a
reference pressure. The reference pressure can be provided as a
static pressure at a location shielded from the wind. By virtue of
the present invention, measurements can be obtained at high speed
so that both high sensitivity and fast response necessary for
turbulence measurements may be had.
The present invention converts the aforementioned dynamic and
static pressures to acoustical waves to be detected by a microphone
which, with acoustical and electronic processing techniques,
provides a very sensitive output. The conversion is implemented by
mechanically alternating between two ports respectively connected
to the dynamic pressure orifice and the reference pressure orifice.
The resulting signal is an acoustical wave. The signal is then
passed into a microphone and then processed electronically for a
readout indication. The entire acoustical system is designed to
obtain the requisite high sensitivity and time response.
Sensitivity may be increased greatly by using phase-sensitive
amplification of the electrical signal from the microphone. The
previously mentioned mechanical switching between two ports is
accomplished by utilizing a rotor with passages formed
therethrough. A standard photo-optic rotor pickup detects the
rotational rate and phase of the rotor which corresponds to the
rotational rate and phase of electrical signals due to the
acoustical signals picked up by the microphone. Utilizing the
photo-detector output as a second input to the phase sensitive
amplifier, amplification of only the AC component of the signal,
which has a fixed phase relationship to that of the rotor, is
processed. A readout is connected to the output of the amplifier
for indicating flow rates with great sensitivity and fast response
time.
The above-mentioned objects and advantages of the present invention
will be more clearly understood when considered in conjunction with
the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a cut-away view of the inventive sensor.
FIG. 2A is a cross sectional view taken along a plane passing
through section line 2A--2A of FIG. 1 with the sensor rotor in
position for measuring dynamic wind pressure.
FIG. 2B is a view similar to that of FIG. 2A but with the rotor
displaced 90.degree. for effective measurement of static
pressure.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the figures and more particularly FIG. 1 thereof, the
apparatus of the present invention is seen to include a sensor 10
to which a motor 12 is mounted. The motor shaft 14 extends inwardly
of the sensor housing 15 for connection to a rotor shaft 18 via a
coupling 20, which may be a flexible coupling of conventional
design. The rotor 16 is centrally located within housing 15 and is
supported at its ends in bearings 22 and 24. The rotor acts as a
flow switch as will be seen from the following description of FIG.
2A. A tube 30 is axially directed toward an air stream so that the
sensor can measure the dynamic pressure caused by its flow. The
dynamic pressure is convertible to an airflow rate using a known
mathematical relationship. In a typical atmospheric environment,
airflow rates, or their fluctuations, may be quite small. A pitot
tube 28 serves as the simplest form of inlet while the opposite
tube end 26 is an outlet for directing the flow into orifice 32
formed in the sensor housing. The orifice 32 communicates with
radially oriented air passage 34 in the housing and in the position
of rotor 16 as indicated in FIG. 2A, the curved air passageway 36
forms a conduit between air passage 34 and a second air passage 38
which is located 90.degree. from the air passage 34. An orifice 40
is formed at the radially outward end of air passage 38 for
registry with an orifice 42 formed in an enclosure for microphone
44. In the position illustrated in FIG. 2A, output will be
discussed hereinafter.
FIG. 2B illustrates the position of rotor 16 when it has been
rotated 90.degree.. As will be observed, passageway 36 now
communicates between orifice 40 and orifice 50. A second tube 54 is
positioned in registry with orifice 50, the tube 54 communicating
static pressure to the microphone 44. This is accomplished by
inserting an outward end 56 of tube 54 in a shield with baffle 58.
Thus, the static pressure condition in the shield 58 is
communicated between the tube outlet 52, the air passage orifice 50
and passageway 36 to microphone 44. Thus, microphone 44 has sensed
a net acoustical wave derived in first part from the air flow
condition creating a dynamic pressure in tube 30, and in second
part from the static air pressure in tube 54.
A second passageway 46 is seen to exist in rotor 16. The
passageways may be likened to two oppositely directed elbow
configurations. During the 90.degree. rotation discussed in
connection with FIGS. 2A and 2B, the second passageway 46 is
inoperative. However, upon a further rotation of rotor 16 in a
clockwise direction by 90.degree. (not shown), the passageway 46
will serve to connect the air flow through tube 30 to microphone 44
once again, as in FIG. 2A. Then upon a further 90.degree.
displacement of rotor 16 (not shown), the second passageway 46 will
connect the static air pressure in tube 54 to the microphone 44, as
in FIG. 2B. Thus, microphone 44 alternately receives dynamic air
flow data from tube 30 and static air reference data through tube
54, twice per complete rotation of rotor 16.
Referring back to FIG. 2A, the block diagram for electronic signal
processing is seen to include a conventional phase-locked amplifier
60 having a first input connected to microphone 44. In order to
provide rotor phase information to this amplifier, a conventional
photo-optic pickup is mounted within housing 15 as will be seen in
FIG. 1. Specifically, an LED 62 is positioned in optical alignment
with a detector 68 which may be a silicon detector. Rotor extension
66 is axially disposed in the housing and in optical interference
between the LED optical source 62 and detector 68. A bore 64 is
formed along the diameter of the extension 66 so that detector 68
detects light from LED 62 twice during each full rotation of rotor
16. It is the electrical output from detector 68 which forms the
second input of the amplifier 60 shown in FIG. 2A. The amplifier
60, of conventional design, amplifies only the AC component of the
microphone signal which has a fixed phase relationship to that of
the rotor. This increases the signal-to-noise ratio of the
electrical processing considerably. The output of the phase-locked
amplifier 60 may be connected to a conventional analog-to-digital
converter 72 which in turn drives a digital readout 74 indicating
the measurement of dynamic airflow presented at tube 30. Of course,
in the event an analog meter is to be used, and A/D converter is
unnecessary.
The signal processing exhibits a time response which is some
fraction of rotor speed. In order to minimize the time response,
one may eliminate the phase-locked amplifier and instead use a
conventional peak detector, followed by a timed conversion to
digital signals for direct input to a computer. In this case,
although there is no diminishing of the time response, the
signal-to-noise ratio would be lower.
The rotor described in the present invention may be machined in two
halves with the air passageways 36 and 46 formed with a ball end
mill so as to make perfectly smooth transitions as the rotor
rotates.
Further, although the dynamic pressure port has been prestated as a
pitot tube 28 and the static pressure reference port has been
explained as utilizing a baffled port 58, orifices 56 and 28 may
consist of similar and oppositely directed pairs of ports such as
pitot tubes or holes in opposite sides of a sphere. This allows the
magnitude of the wind component along the axis of the orifices 32
and 50 to be measured regardless of its sign. When the sign of the
component changes, the designation of the orifices 32 and 50 also
changes. The amplitude of the resulting output signal at microphone
44 is only dependent on the absolute value of the pressure
difference (i.e., magnitude of the air flow component), not the
sign. The sign information is contained in the phase of the wave
signal. A change in sign of the pressure difference (i.e., the sign
of the wind component) causes a 180.degree. shift in the output
wavefrom. One of the outputs of amplifier 60 is A cos .theta. where
A is the amplitude and .theta. is the phase of the output signal.
This allows both the magnitude and sign of the wind component to be
easily measured using the amplifier 60.
Accordingly, the above-described invention offers apparatus for
high sensitivity and fast response manometric air flow/pressure
sensing where air flow rates (including very low flow rates) of
wind or turbulence are to be measured.
It is emphasized that although the invention is described in terms
of air flow measurements, it is equally applicable for other
gases.
It should be understood that the invention is not limited to the
exact details of construction shown and described herein for
obvious modifications will occur to persons skilled in the art.
* * * * *